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rATE PLANT BOARD
August 1952 E-843
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
THE RELATIVE TOXICITY TO HOUSE FLIES OF ENDRIN AND
ISODRIN IN KEROSENE SPRAYS
By W. A. Gersdorff, Norman Mitlin, and R. H. Nelson
Division of Insecticide Investigations
Two compounds closely related to dieldrin and aldrin have recently
shown promise as insecticides. They have been designated by the manu-
facturer as compounds 269 and 711, but will be known hereafter as endrin
Samples of these materials were obtained for preliminary evaluation
of toxicity. Although of technical grade, they were crystalline. The
sample of endrin was slightly brownish and that of isodrin white; the
former was 84 percent and the latter 95 percent pure. They were not
further purified. A purified sample of aldrin (m.p. 95 -98° C.) was used
as a standard of comparison because of its close chemical relationship
to these compounds. Pyrethrins, the common standard for space sprays,
was also included in the study; it contained 52 percent of pyrethrin I and
Stock solutions of the materials in refined kerosene were prepared.
To insure a prompt and complete solution, acetone was used as an auxiliary
solvent. It was particularly needed for the less soluble endrin. After
preliminary tests, these stock solutions were further diluted with kerosene
to form sprays containing four concentrations of each material that would
give a range of mortalities of test insects to extend over the 50-percent
point. The highest concentration of acetone in the sprays was 1.5 percent
by volume. This concentration has not been found to have a measurable
effect on the mortality caused by a number of materials tested by this
The test insect was the house fly ( Musca domestica L.). Knockdown
and mortality were determined by the Campbell turntable method. Eight
replications were made, all sprays being tested in duplicate against each
of four populations of flies; approximately 90 flies averaging 2 1/2 days in
age were used in each test.
- 2 -
To evaluate relative toxicity and determine the precision of the
estimates, the mortality data were subjected to probit analysis as
described by Finney (1).
Knockdown and Mortality
Knockdown of flies was complete for the pyrethrins sprays, as is
usual by this method at the concentrations used. All the other sprays
caused no knockdown. The mortality data are summarized in table 1.
They show that the samples of endrin and isodrin did not differ greatly
in toxicity, if at all, and were substantially less toxic than aldrin but
much more toxic than pyrethrins.
Table 1. --Relative toxicity to house flies of endrin, isodrin, aldrin,
and pyrethrins in kerosene sprays
in 1 day
Mg. per dl.
Mg. per dl.
Evaluation of Relative Toxicity
Analysis showed that, when probits were plotted against log concen-
trations, the data for endrin, isodrin, and aldrin could be represented by
parallel lines. Therefore, a generalization procedure as described by
Finney (1) was used, the common regression coefficient being 3.35+0.12
probits per unit log concentration. Since the slope of the line representing
the data for pyrethrins was significantly different, the data for this mate-
rial were not included in the generalization; the regression coefficient of
the individually fitted line for pyrethrins was 2.36+0.32. Heterogeneity
between populations of flies was great enough to result in significant
chi-squares measuring departures from linearity for isodrin and
pyrethrins. Therefore, all variances obtained in the determination
of the precision of the estimates were multiplied by a heterogeneity
factor; this factor for the pooled chlorinated hydrocarbons was 2.23
and for pyrethrins 3.20.
The statistically computed equations showing the regression of
mortality, expressed in probits, on concentration in milligrams per
deciliter, expressed as logarithms, are as follows:
Endrin Y = 3.3506 X + 0.8360
Isodrin Y = 3.3506 X + 0.6915
Aldrin Y = 3.3506 X + 1 .4136
Pyrethrins Y = 2.3636 X - 0.7282
From these equations the median lethal concentrations (LC-50's)
were calculated. Relative toxicity was then determined as the inverse
ratios of LC-50's. These estimations and their standard errors are
also given in table 1.
Statistical analysis showed the difference in the relative toxicities
of endrin and isodrin to be significant.
The sample of endrin was 67 percent as toxic as aldrin and, according
to the ratio of the toxicity of aldrin to that of dieldrin (0.68) found previ-
ously by this method (Gersdorff et al. 2), 46 percent as toxic as dieldrin.
The sample of isodrin was 61 percent as toxic as aldrin.
At the median lethal concentration the samples of endrin, isodrin,
and aldrin were 15, 14, and 23 times as toxic as pyrethrins. The last
ratio agrees very well with those obtained in two earlier comparisons
of aldrin and pyrethrins by this method (Gersdorff et al. 2).
Endrin, isodrin, and aldrin caused no knockdown at the concentra-
UNIVERSITY OF FLORIDA
3 1262 09239 6398
(1) Finney, D. J.
1947. Probit analysis. 256 pp. Cambridge.
(2) Gersdorff, W. A., Nelson, R. H., and Mitlin, Norman
1950. The relative toxicity of heptachlor, aldrin, and dieldrin to
house flies when applied as space sprays using Campbell
turntable method. Soap and Sanit. Chem. 26(4): 137, 139